1. Field of the Invention
The present invention relates to an active element for a battery whose material contains a copper oxyphosphate and an additive which improves the conductivity. The present invention also relates to a method for producing an active element of this type. In addition, the invention relates to a battery and a method for the production thereof.
2. Description of the Related Art
A battery is an electrochemical energy store, whose stored chemical energy is converted by an electrochemical redox reaction into electrical energy. Because of different requirements for batteries in regard to voltage, power, internal resistance, and capacitance, for example, manifold different battery types currently exist. The properties of the batteries are essentially influenced by the composition of the material of the active elements of the batteries.
The term “active element” is used hereafter in general for an electrode of the battery, i.e., cathode or anode.
Materials for positive active elements of batteries which contain copper oxyphosphate are known from the publications cited below. The term copper oxyphosphate hereafter includes the compoundCunOp(PO4)2 with 3<n≦6 and p=(n−3),n=4 being preferred. A cathode having copper oxyphosphate is preferably used in a battery together with an anode which comprises lithium. A solution which does not contain water and in particular comprises a lithium compound in a non-aqueous solvent or solvent mixture is frequently used as the electrolyte.
A material for a positive active element of a battery and a method for producing this active element are known from the publications DE 10 2006 021 158 A1, DE 10 2006 059 375 A1, and U.S. Pat. No. 4,260,668. The material of the positive active element predominantly comprises copper oxyphosphate Cu4O(PO4)2 as the active material, carbonaceous conductivity additives such as graphite, and fluoridated binders, such as polytetrafluoroethylene (PTFE). This compound was compacted to form an anode or cathode. The copper oxyphosphate was previously produced by dehydrating a hydroxyphosphate at various temperatures (590° C., 600° C., 620° C., and 900° C.).
The publication U.S. Pat. No. 4,448,864 discloses a lithium-manganese dioxide battery whose positive electrode also contains copper oxyphosphate and graphite as well as PTFE as a binder, in addition to manganese dioxide. The proportion of the copper oxyphosphate in the composition of this electrode is 10 wt. % in an example described in this publication. Due to the proportion of the copper oxyphosphate, a second plateau is reached at approximately a voltage of 2.2 V to 2.3 V during the discharge of the battery, the extent of the plateau being determined by the quantity of the copper oxyphosphate in the material of the positive electrode.
For use in medical implants having electronic components for a human or an animal, such as cardiac pacemakers, which are to be provided with wireless, preferably bidirectional data transmission, batteries are required which have a high capacitance on one hand and allow high discharge currents in the mA range to be drawn on the other hand. A high capacitance of the battery lengthens the usage time of the medical implant and thus decreases the number of surgical interventions, because replacing the battery and/or inserting a new implant having a fully charged battery is typically connected to a surgical intervention. A higher discharge current is required for providing higher currents for data transmission.
The cathode materials for lithium primary batteries described in the above-mentioned publications have the disadvantage that the batteries equipped therewith do not have a higher discharge capacitance than the currently used lithium-iodine batteries. In contrast, currents in the mA range may not be drawn from lithium-iodine batteries.